Billing: Add feature to calculate member/delivery bins

Elwig/Helpers/Billing/BillingVariant.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Elwig.Helpers.Billing {
+    public class BillingVariant : Billing {
+
+        private readonly int AvNr;
+
+        public BillingVariant(int year, int avnr) : base(year) {
+            AvNr = avnr;
+        }
+
+        protected async Task DeleteInDb() {
+            using var cnx = await AppDbContext.ConnectAsync();
+            using (var cmd = cnx.CreateCommand()) {
+                cmd.CommandText = $"DELETE FROM payment_delivery_part WHERE (year, avnr) = ({Year}, {AvNr})";
+                await cmd.ExecuteNonQueryAsync();
+            }
+            using (var cmd = cnx.CreateCommand()) {
+                cmd.CommandText = $"DELETE FROM payment_member WHERE (year, avnr) = ({Year}, {AvNr})";
+                await cmd.ExecuteNonQueryAsync();
+            }
+        }
+
+        public async Task CalculatePrices() {
+            await DeleteInDb();
+            var tasks = new List<Task>();
+            foreach (var mgnr in Context.Members.Select(m => m.MgNr)) {
+                tasks.Add(Task.Run(() => CalculateMemberPrices(mgnr)));
+            }
+            await Task.WhenAll(tasks);
+        }
+
+        protected async Task CalculateMemberPrices(int mgnr) {
+
+        }
+    }
+}